Abstract: Disclosed are a method and an apparatus for easily, sensitively and reliably detecting the presence of a magnetic substance in a non-magnetic product, and even a minuted magnetized material such as a broken needle erroneously included in a sewn product. Magnetic sensors as a sensing unit are disposed at a prescribed position between a pair of opposed magnetic shielding members made of a soft magnetic material as a magnetic flux converging unit. A non-magnetic product including a magnetic substance is passed through between the pair of magnetic shielding members. A magnetic flux generated by the magnetic substance mingled in the product is converged to the magnetic shielding members, while shutting off a magnetic field due to external disturbance, and residual magnetization of the magnetic substance is detected by the magnetic sensors.

Abstract: Disclosed are a method and apparatus for detection of a magnetic substance erroneously included in a non-magnetic product. The non-magnetic product such as a sewn product is passed through a high magnetic field in which a magnetic field is applied to the product. The residual magnetization of a magnetic substance such as a broken needle mingled in the product is detected by a sensing unit and a signal of detection is transmitted to a measuring unit to measure the magnitude of detected residual magnetization. The presence or absence of the magnetic substance in the product is determined by a control unit based on the output from the measuring unit. Alternatively, a magnetic field may be preparatorily applied to a magnetic substance having the possibility of being mingled in the non-magnetic product thereby causing the magnetic substance to assume a state of possessing residual magnetization.